1. Field of the Invention
The present invention relates to an Si—SiC based fired body and a method for manufacturing the same. More particularly, it relates to an Si—SiC based fired body that is resistant to oxidation degradation, breakage, and the like even when a thick-walled shape is taken and a method for manufacturing the same.
2. Description of the Related Art
Heretofore, silicon carbide (SiC) based fired bodies have held an industrially important position because of their excellent heat resistance and fire resistance, and have been used frequently as, for example, shelf boards for firing ceramics such as insulators, sanitary earthenware, tableware, frame, and pottery tubes, and tiles. Among these SiC based fired bodies, Si—SiC based fired bodies containing SiC and Si as constituent components have been primarily used as furnace tubes for firing semiconductors, tubes for roller heat exchangers of roller hearth kilns, shelf boards for firing ceramic products, and the like (for example, refer to Japanese Patent No. 2758313, Japanese Patent No. 2535480, and Japanese Patent No. 3137737).
There is a problem in that when thicknesses of these Si—SiC based fired bodies are increased, strength and oxidation resistance cannot be maintained. The Si—SiC based fired body is produced by impregnating a porous SiC fired body with metal silicon (Si). When the SiC fired body takes a thick-walled shape having a thickness of 20 mm or more, metal Si is not easy to impregnate therein, and therefore many pores not filled with metal Si remain in the Si—SiC based fired body. In this case, there are cracking problems that occur during the production and accordingly, the strength decreases significantly due to pores. Furthermore, when an Si—SiC based fired body having many remaining pores is used under a high temperature, there is a problem in that oxidation degradation proceeds from portions of pores, the strength decreases, and snap, breakage, and the like may occur.
Heat-resistant materials other than the Si—SiC based fired bodies, such as oxide-bonded SiC materials, silicon nitride-bonded SiC materials, and alumina-mullite materials, can take thick-walled shapes. However, under an environment in which a large temperature difference occurs, there is a problem in that a thermal stress, which causes destruction, is generated due to the temperature difference, since the thermal conductivity is low. When an increase and a decrease in temperature are repeated during use, a stress due to repetition is generated and, thereby, damage or destruction occurs due to cyclic fatigue. Furthermore, there is a problem in that damage due to mechanical stress can occur easily since the strength of the bonding structure is low and a life span becomes short since the abrasion resistance and the like are low.
Monolithic refractories are notable for good workability, low cost, and the like. However, as in the case of the above-described oxide-bonded SiC materials, there are problems in that breakage can occur at an early stage of use due to the shortage of strength of the bonding structure and damage can occur due to the thermal stress resulting from a temperature difference inside the monolithic refractory.